Bluetooth Antenna Design Matt Shellhammer | October 16th, 2017 | Mattshellhammer90@gmail.com

What is a Bluetooth antenna Devices that are resonant at 2.45 GHz with a bandwidth of more than 100 MHz and an efficiency greater than 50% can be considered a Bluetooth antenna. Due to these broad specifications there is many different forms of antennas for Bluetooth. Wire Monopole – This is a wire that is soldered at one end and fed along a plane and is trimmed to resonate at 2.45 GHz. This type of antenna has high efficiency however protrudes from the PCB. Ceramic — Smallest antennas available. Printed on a ceramic slab. http://www.nienyi.com/e_channel.asp?id=44 https://electronics.stackexchange.com/questions/243341/how-does-a-chip-antenna-work

Other Various Antenna Types Wire Antennas Loop antenna Dipole antenna (Special case: Half- wave dipole antenna) Travelling Wave Antennas Reflector Antennas Microstrip Antennas Rectangular Microstrip (Patch) Antenna Log-Periodic Antennas Aperture Antennas Slot antenna Other Wearable antenna

Ceramic antennas The big advantage of ceramic antennas are that they are small. There small size is attributed to their high dielectric constant (high-κ) which concentrates its electric field and therefore maintain a high resonant frequency. Size of ceramic antenna: 𝜆 0 𝜖 𝑟 𝜆 0 : free-space wavelength 𝜖 𝑟 : Dielectric constant - Metal parts become lossy at high frequencies and dissipate energy. Chosing a high dielectric constant will allow for a relatively small device. Dipole antennas are most commonly referring to half-wavelength. Therefore the size of a dipole antenna is 𝜆/2 so for Bluetooth at 2.45 GHz a dipole antenna would be 61.2 mm https://www.researchgate.net/figure/237054209_fig1_Figure-1-A-rectangular-Dielectric-resonator-antenna-geometry

Additional benefits of Dielectric resonator (ceramic) antennas Dielectric resonator (ceramic) antennas (DRA) lack metal parts. Because of this, they can have higher efficiency than metal antennas at higher frequencies. The Bandwidth of a DRA can be easily varied from a fraction of a percent to approximately 20%. “The operating bandwidth of a DRA can be varied over a wide range by suitably choosing resonator parameters. For example, the bandwidth of the lower order modes of a DRA can be easily varied from a fraction of a percent to about 20% or more by the suitable choice of the dielectric constant of the material and/or by strategic shaping of the DRA element.”

PCB (Microstrip) Antennas PCB antennas are traced into the PCB which can reduce the manufacturing costs since it’s included in the PCB assembly process. PCB antennas are thin, simple and generally have fairly large bandwidth. Small changes or tolerance variations within PCB manufacturing process can result in an offset center frequency which can cause frequency shifting. Though the PCB manufacturing process is fairly reliable these very minuscule variations can have a large effect on the antenna due to the inherit nature of antennas being sensitive devices. https://e2e.ti.com/support/wireless_connectivity/nfc_rfid/f/667/t/496205

Ceramic vs PCB Ceramic antennas have less significant detuning issues when placed in close proximity to other component. Ceramic antennas are effected less by environmental factors (obstructions) than PCB antennas. PCB antennas are limited on tuning options, ceramic antennas can simply use a matching circuit. PCB antennas take up space on the PCB that could be used for other components.

Antenna Radiation Free space path loss, 𝐹𝑆𝑃𝐿= 4 𝜋 𝑑 𝜆 2 , will be consistent for all Bluetooth antennas since they’re all operating at the same frequency. However, each antenna will have its own radiation pattern. What is most desired for our applications is an omnidirectional antenna radiation pattern. Radiation pattern should be taken into account when thinking about what applications the antenna will be used for. The reason for the frequency dependence is that the equation contains two effects: The first results from the spreading out of the energy as the sphere over which the energy is spread increases in area. This is described by the inverse square law. The second effect results from the antenna aperture change. This affects the way in which any antenna can pick up signals and this term is frequency dependent.

Beamforming Directional beamforming is the process of focusing a signal in a specific direction to improve the signal strength in the path of the beam. Applications: wireless communications, radar, sonar, etc. This technique can all be used to implement spatial filtering For our applications beamforming is not desired. This is possible due to constructive and destructive interference. http://www.sharetechnote.com/html/Handbook_LTE_BeamForming.html

References www.ti.com/lit/an/snoa519b/snoa519b.pdf http://www.antenna-theory.com/antennas/main.php https://en.wikipedia.org/wiki/Dielectric_resonator_antenna https://www.researchgate.net/figure/237054209_fig1_Figure-1-A-rectangular- Dielectric-resonator-antenna-geometry https://www.digikey.jp/Web%20Export/Supplier%20Content/Pulse_553/PDF/pulse_cer amic-chip-antennas-vs-pcb-trace-antennas.pdf

Bluetooth Loss-of-Signal (LoS) Experiment

Experiment Layout Captured Bluetooth signal power levels using the “BLE Scanner” app from the google play store. Rotated around the board at various radii and recorded the power level at each point in space. Set “BLE Scanner” app to scan for 8 seconds.

Results at radius: 1 foot

Results at radius: 4 feet

Results at radius: 8 feet

Results at radius: 12 feet

Full 3D space of experiment Red: radius = 1 foot Blue: radius = 4 feet Green: radius = 8 feet Purple: radius = 12 feet

Experiment Data Didn’t do the last two columns because the phone would have had to be 6.9 & 10.4 feet in the air and that wasn’t feasible.

Thanks For Listening

Questions

Questions 1-6 What is the resonant frequency of a Bluetooth antenna? 5 GHz 2.45 GHz 3.45 GHz 950 MHz What is the minimum bandwidth for a device to be considered a Bluetooth device? 100 kHz 500 kHz 150 MHz 100 MHz Which type of the following antennas is the smallest antenna available? Loop antenna Microstrip (patch) antenna Dipole antenna Dielectric resonator (ceramic) antenna What is a benefit of a PCB antenna? Reduced manufacturing costs Objects don’t interfere with signal Easy tuning process to improve antenna performance. They have an efficiency of 95% Which antenna allows for more components to be used on the PCB? Ceramic antenna PCB antenna Which frequency will have the greatest Free Space Path Loss (FSPL)? 1 GHz 2.45 GHz 10 GHz 200 MHz

Questions 1-6 Answers What is the resonant frequency of a Bluetooth antenna? 5 GHz 2.45 GHz 3.45 GHz 950 MHz What is the minimum bandwidth for a device to be considered a Bluetooth device? 100 kHz 500 kHz 150 MHz 100 MHz Which type of the following antennas is the smallest antenna available? Loop antenna Microstrip (patch) antenna Dipole antenna Dielectric resonator (ceramic) antenna What is a benefit of a PCB antenna? Reduced manufacturing costs Objects don’t interfere with signal Easy tuning process to improve antenna performance. They have an efficiency of 95% Which antenna allows for more components to be used on the PCB? Ceramic antenna PCB antenna Which frequency will have the greatest Free Space Path Loss (FSPL)? 1 GHz 2.45 GHz 10 GHz 200 MHz

Questions 7-10 All antennas have the same radiation pattern. True False Omnidirectional antennas are useful for spatial filtering. Which is not an application of beamforming? Wireless communications Radar Microcontroller robots Sonar Generally what is the length of a dipole antenna? 4λ 2λ λ/2 λ

Questions 7-10 Answers All antennas have the same radiation pattern. True False Omnidirectional antennas are useful for spatial filtering. Which is not an application of beamforming? Wireless communications Radar Microcontroller robots Sonar Generally what is the length of a dipole antenna? 4λ 2λ λ/2 λ